TITLE:   GCN CIRCULAR
NUMBER:  19360
SUBJECT: Fermi/LAT search for counterpart to the IceCube event 67093193 (run 127853)
DATE:    16/04/28 22:38:47 GMT
FROM:    Giacomo Vianello at SLAC  <giacomov@slac.stanford.edu>

G.Vianello (Stanford), J. D. Magill (UMD/GSFC), N. Omodei (Stanford), D.
Kocevski (NASA/Goddard), M. Ajello (Clemson), S. Buson (NASA/GSFC), F.
Krauss (ECAP/FAU), J. Chiang (SLAC/Kipac)

report on behalf of the Fermi-LAT team:

We have searched the Fermi Large Area Telescope data for a high-energy
gamma-ray counterpart for the IceCube High Energy Starting Event (HESE)
67093193, detected in run 127853 on 2016-04-27 05:52:32.00 UT (AMON GCN
notice rev. 2, http://gcn.gsfc.nasa.gov/notices_amon/67093193_127853.amon.
See http://gcn.gsfc.nasa.gov/doc/Public_Doc_AMON_IceCube_GCN_Alerts_v2.pdf
for a description of HESE events and related GCN notices).

The localization region was outside the LAT field of view at the time of
the detection by IceCube (T0). It entered the LAT FoV at ~T0 + 6140 s and
exited again at ~T0 + 8420 s. We ran the standard GRB search (Vianello et
al. 2015) plus an ad-hoc search for a counterpart in this time interval and
in 10 h intervals before and after the event. We found no significant
transient candidate associated with the neutrino event.

The Automated Science Processing search, which looks for variation in flux
from known sources and for new transients on different time scales (Chiang
2012), did not detect any transient or flaring source consistent with the
IceCube event position during the six-hour intervals before and after the
neutrino detection time, nor during the day before and after the event.

The Fermi All-Sky Variability Analysis (FAVA), a photometric analysis
currently designed to detect variable sources on one-week timescales, did
not find any excess emission consistent with the most current
localization.  Likewise, an examination of previous weeks analyzed by
this technique reveals no long timescale flaring sources compatible with
the localization region.

The 90% containment provided by IceCube, which is ~36 arcmin wide, contains
no LAT source from the Fermi Point Source catalog (3FGL, Acero et al.
2015). The 5 closest sources are all blazars:

Source name       | Distance | Association           | Blazar Type |
--------------------------------------------------------------------
3FGL J1603.7+1106 | 108'     | MG1 J160340+1106      | BL Lac      |
3FGL J1608.6+1029 | 117'     | 4C +10.45             | FSRQ        |
3FGL J1555.7+1111 | 147'     | PG 1553+113           | BL Lac      |
3FGL J1552.1+0852 | 153'     | TXS 1549+089          | BL Lac      |
3FGL J1546.0+0818 | 249'     | 1RXS J154604.6+081912 | BL Lac      |

We note in particular that PG 1553+113 has been detected in high state on
2016-04-27 in the 0.3-10 keV band by the Swift X-ray Telescope (B.
Kapanadze, ATel #8998, http://www.astronomerstelegram.org/?read=8998),
although we do not detect any significant change in flux above 100 MeV.

The Fermi-LAT points of contact for this event are Giacomo Vianello (Burst
Advocate, giacomov@stanford.edu) and Jeffrey D Magill (Flare Advocate,
jmagill@umd.edu).

The Fermi-LAT is a pair conversion telescope designed to cover the energy
band from 20 MeV to greater than 300 GeV. It is the product of an
international collaboration between NASA and DOE in the U.S. and many
scientific institutions across France, Italy, Japan and Sweden.